Cells as the basic units of living organisms
Cambridge A-Level Biology (9700) · Unit 1: Cell structure · 18 flashcards
Cells as the basic units of living organisms is topic 1.2 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 1 — Cell structure , alongside The microscope in cell studies. In one line: The cell surface membrane is a phospholipid bilayer with embedded proteins. Its main function is to regulate the movement of substances into and out of the cell, providing a selective barrier.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 18 flashcards — 15 definitions and 3 key concepts — covering the precise wording mark schemes reward. Use the 15 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Describe the structure and primary function of the cell surface membrane
The cell surface membrane is a phospholipid bilayer with embedded proteins. Its main function is to regulate the movement of substances into and out of the cell, providing a selective barrier.
What the Cambridge 9700 syllabus says
Official 2025-2027 spec · AS LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- describe and interpret photomicrographs, electron micrographs and drawings of typical plant and animal cells
- compare the structure of typical plant and animal cells
- state that cells use ATP from respiration for energy-requiring processes
- outline key structural features of a prokaryotic cell as found in a typical bacterium, including: • unicellular • generally 1–5 µm diameter • peptidoglycan cell walls • circular DNA • 70S ribosomes • absence of organelles surrounded by double membranes
- compare the structure of a prokaryotic cell as found in a typical bacterium with the structures of typical eukaryotic cells in plants and animals
- state that all viruses are non-cellular structures with a nucleic acid core (either DNA or RNA) and a capsid made of protein, and that some viruses have an outer envelope made of phospholipids
- www.cambridgeinternational.org/alevel
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Cells as the basic units of living organisms
- › Use the term 'nuclear envelope' specifically when referring to the double membrane visible in electron micrographs.
- › Always double-check unit conversions; remember that 1 millimetre (mm) is equal to 1000 micrometres (μm) when calculating actual size.
- › Recall that endosymbiosis means mitochondria and chloroplasts possess 70S ribosomes and circular DNA, distinct from the eukaryotic 80S ribosomes.
- › Recognize that individual molecules are generally too small to be seen in standard TEM images; identify organelles like Smooth ER instead.
- › Remember that organelles like centrioles and ribosomes are too small to be observed with a conventional light microscope at standard school magnifications.
Describe the structure and primary function of the cell surface membrane.
The cell surface membrane is a phospholipid bilayer with embedded proteins. Its main function is to regulate the movement of substances into and out of the cell, providing a selective barrier.
What is the role of the nucleolus within the nucleus?
The nucleolus is a structure within the nucleus responsible for ribosome synthesis. It assembles ribosomal RNA (rRNA) and proteins to form ribosomal subunits.
Distinguish between the functions of rough and smooth endoplasmic reticulum (ER).
Rough ER contains ribosomes and is involved in protein synthesis and modification. Smooth ER lacks ribosomes and is involved in lipid synthesis, carbohydrate metabolism, and detoxification.
Outline the structure and function of the Golgi body (Golgi apparatus).
The Golgi body is a stack of flattened membrane-bound sacs called cisternae. It modifies, sorts, and packages proteins and lipids synthesized in the ER for transport to other organelles or secretion.
Describe the structure of a mitochondrion, including the significance of its circular DNA.
Mitochondria have a double membrane; the inner membrane is folded into cristae. They contain their own circular DNA, encoding some mitochondrial proteins, which supports the endosymbiotic theory.
What is the function of ribosomes, and where are 80S and 70S ribosomes found?
Ribosomes are responsible for protein synthesis (translation). 80S ribosomes are found in the cytoplasm of eukaryotic cells, while 70S ribosomes are found in prokaryotes, chloroplasts, and mitochondria.
Describe the role of lysosomes in eukaryotic cells.
Lysosomes contain hydrolytic enzymes. They break down cellular waste, debris, and foreign materials through phagocytosis and autophagy, playing a crucial role in intracellular digestion.
What are the functions of centrioles and microtubules in cell division and structure?
Centrioles organize microtubules, forming the spindle fibers during cell division. Microtubules provide structural support, facilitate intracellular transport, and form cilia and flagella.
Describe the structure and function of chloroplasts, highlighting the role of their circular DNA.
Chloroplasts are organelles in plant cells responsible for photosynthesis, containing chlorophyll. Their circular DNA encodes some of the proteins needed for their function, also supporting the endosymbiotic theory.
What are plasmodesmata and their function in plant cells?
Plasmodesmata are channels that cross plant cell walls, connecting the cytoplasm of adjacent cells. They allow for the transport of water, nutrients, and signaling molecules between cells.
Describe the key structural differences between typical plant and animal cells.
Plant cells possess a cell wall, chloroplasts, and a large central vacuole, which are absent in animal cells. Animal cells have centrioles and lack a cell wall and chloroplasts.
What is the function of ATP in cells?
ATP (adenosine triphosphate) provides energy for cellular processes. It releases energy through hydrolysis, driving energy-requiring reactions such as muscle contraction and active transport.
Outline the key structural features of a prokaryotic cell as found in a bacterium.
Prokaryotic cells are unicellular, generally 1–5 µm in diameter, possess a peptidoglycan cell wall, circular DNA, 70S ribosomes, and lack membrane-bound organelles.
Compare the ribosomes found in prokaryotic and eukaryotic cells.
Prokaryotic cells contain 70S ribosomes, while eukaryotic cells contain larger 80S ribosomes. 'S' refers to Svedberg units, a measure of sedimentation rate during centrifugation.
Describe the structure of a virus.
Viruses are non-cellular structures consisting of a nucleic acid core (DNA or RNA) surrounded by a capsid made of protein. Some viruses also have an outer envelope made of phospholipids.
What type of genetic material is found in viruses?
Viruses contain either DNA or RNA as their genetic material. This nucleic acid is enclosed within a protein capsid.
Identify three structures present in plant cells but absent in animal cells.
Plant cells contain chloroplasts, a cell wall (composed of cellulose), and a large central vacuole, which are not found in animal cells.
Describe the composition of a bacterial cell wall.
Bacterial cell walls are primarily composed of peptidoglycan, a polymer consisting of sugars and amino acids. This provides structural support and protection for the cell.
More topics in Unit 1 — Cell structure
Cells as the basic units of living organisms sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Cells as the basic units of living organisms deck
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